In pumps the medium to be conveyed, that is to say to be pumped, is usually employed directly as a coolant for the drive motor of the pump. When dealing with sewage or waste water or other contaminated fluids that can result in blockage of the cooling volume of the drive motor. In addition pumps and in particular sewage pumps are known, which have an internal cooling system for their drive motor. In such an arrangement circulation of the coolant is effected by an additional small coolant impeller. That coolant impeller can be operatively connected to its own small electric motor. Another possible option involves driving the above-mentioned small coolant impeller directly by the pump drive motor. In that case either the coolant impeller is provided at the free end of the drive shaft of the drive motor, associated with the pump impeller, or the drive shaft of the drive motor is prolonged on the side remote from the free shaft end thereof and the coolant impeller is disposed on the side of the drive motor, which is remote from the pump impeller. In those known pumps, irrespective of the respective arrangement of the coolant impeller, it is necessary for the coolant circuit to be sealed off in relation to the drive motor and possibly the medium being conveyed, that is to say sewage, by means of dynamic seals. Dynamic seals however are subject to leakage which cannot be reliably excluded. Such leakage results for example in the danger that, in the extreme case, the cooling system fails or coolant penetrates into the drive motor.
CH 614 760 A5 discloses a canned centrifugal pump having a magnetic coupling whose outer part which surrounds the can and whose inner part which is surrounded by the can are provided with bar-shaped permanent magnets which are disposed in axis-parallel mutually juxtaposed relationship. The pump casing, the rotor of the canned centrifugal pump and the inner coupling part of the magnetic coupling preferably comprise a temperature-resistant and/or acid-resistant plastic material in order to provide a powerful, gland-less chemical canned centrifugal pump which makes it possible to achieve operationally reliable protection from corrosion. The side faces and the end faces of the permanent magnets which are completely embedded in the inner coupling part converge outwardly. Bearing substances are embedded in the plastic material, in the region of the bearing surfaces of the interconnected parts of the magnetic coupling. In that known canned centrifugal pump the permanent magnet coupling serves for mechanically coupling the pump drive motor to the pump impeller.
A canned centrifugal pump with a permanent magnet coupling is also known for example from DE 33 37 086 C2. That known centrifugal pump with a magnetic coupling has a can cup of plastic material which has a reinforcement at least in its axial can region. The can cup of plastic material is enclosed from the outside by a cup-shaped jacket of high-quality steel which serves as a shape stabiliser and holder for the can. In this case also the permanent magnet coupling is provided for connecting the pump drive motor to the pump impeller, in which respect, even at higher pressures and temperatures of the respective medium being conveyed, the can cup of plastic material is of maximum possible stability and good heat dissipation out of the region of the can cup is possible.
DE 36 39 719 C3 describes a canned magnetic pump with a pump casing, a pump impeller and a magnetic coupling having an outer drive part and an inner rotary part magnetically coupled thereto, wherein the outer drive part and the inner rotary part are hermetically sealed from each other by a can cup. A partial flow of the delivery flow of the canned motor pump, which is branched from that delivery flow and which serves to lubricate the pump plain bearings and possibly for dissipating heat losses from the magnetic coupling and bearing heat, is passed through the interior of the can cup. The end, near the pump, of the tube-like part of the can cup has a connecting flange which projects away from the axis of rotation of the magnetic coupling and with which it is fixed to the pump casing. The can cup can be subjected to the action of a heating means which is independent of the medium being conveyed, in order to provide a canned magnetic pump which, while being relatively simple to produce, enjoys a relatively wide range of uses both at high and also at lower temperatures of the medium being conveyed, wherein the can cup affords an enhanced level of security in an accident or damage situation. For that purpose, in that known canned magnetic pump, at least the tube-like part of the can cup is of an at least double-wall configuration and is formed by at least two can walls which are arranged concentrically relative to each other and relative to the axis of rotation of the magnetic coupling. The internal wall space formed by the double or multiple wall structure serves to receive a heating or cooling agent. Provided in the connecting flange which is mechanically firmly and sealingly connected to the can walls are at least one feed passage leading to the internal wall space and at least one discharge passage for the heating agent or coolant. In this known canned magnetic pump the magnetic coupling also serves for operatively connecting the drive motor thereof to the pump impeller.
DE 43 19 619 A1 discloses a submersible motor-driven pump with an electric drive motor, under which is fixed the casing of a centrifugal pump, wherein the casing of the drive motor is coaxially surrounded on the outside by a cooling jacket through which flows the medium to be conveyed. In this case therefore the medium to be conveyed, that is to say to be pumped, is used as a coolant, which—as has been stated in the opening part of this specification—can result in blockage of the cooling jacket when dealing with sewage or waste water or other contaminated fluids. Such a blockage can then lead to overheating of the drive motor and, in the extreme case, total failure thereof.
DE 44 34 461 A1 discloses a submersible motor-driven pump for heavily contaminated fluids. In order to permit cleaning of deposits in the interior of the pump, the submersible motor-driven pump which is provided with a tangential pressure connection and a jacket space which encloses the drive motor and through which the fluid being conveyed flows has a flushing connection which is arranged at the end of the jacket space, that is remote from the pump, the flushing connection being connectable to an external fluid source. The flushing connection is preferably provided with a releasably fixed closure cap provided with a vent system. That represents a structural complication and expenditure which is not to be disregarded.
A cooling unit for cooling submersible mud, sewage and sludge motor-driven pumps for the purposes of dry installation is known from DE 196 40 155 A1. That known cooling unit represents a separate construction without fixed structural connection to the submersible motor-driven pump.
DE 298 14 113 U1 discloses a permanent magnet coupling pump with a pump unit having a rotor which is arranged in a can cup and which is coupled to a driver of a drive unit, which driver extends around the can cup and can be driven in rotation by means of a drive motor. That known permanent magnet coupling pump has a cage which is connected at its one end to the pump unit and which is connected at its opposite end to the drive motor. The driver and the drive motor are drivingly connected by way of a drive means of a material which is a poor conductor of heat. The drive means can be in the form of a coupling or can have a coupling which is interposed into the drive shaft provided between the driver and the drive motor. The coupling is in the form of a dog coupling, an elastomer coupling or a permanent magnet coupling.
The object of the present invention is to provide a drive motor in particular for a pump, which has an internal cooling system which is statically hermetically sealed off.